1. Field of the Invention
The present invention relates to utility knives of the type having a retractable blade and, more particularly, to those having a removable and replaceable blade.
2. Description of the Prior Art
Utility knives tend to have the following characteristics. Retractability of the blade within the casing of the knife provides safety thereto when it is not in use and may also prolong the life of the blade. Sturdiness of the casing of the utility knife and of the blade mounting mechanism is also an important asset if the knife is to be used for heavy duty cutting operations. Removability and replaceability of the blade in the utility knife is an economical feature as the same casing can be used over and over since only the worn blades have to be replaced. Ideally, the blade of such utility knives can be replaced quickly, easily and safely. Two basic casing general designs are basically presently known and used for achieving some of the above-mentioned objects.
The first type of utility knife comprises a casing having two separate complementary halves which are secured together by a screw or by a nut and bolt arrangement. These utility knives thus require tools to disassemble the casing to access the worn blade in order to remove it and replace it with a new one. Furthermore, a certain assembly is required when the two halves of the casing are put back together. Therefore the replacement of a blade for this type of utility knife is time consuming apart from necessitating the usage of tools.
In a second type of utility knife, the two casing halves thereof are pivotally joined one to the other at an end thereof. Means are provided at the end of the casing opposite the pivot to maintain the two halves together when the utility knife is equipped with a functional blade. These means are released and the two halves are then divergingly spread apart in order to access the interior of the knife to replace the worn blade contained therein. Such utility knives are disclosed in U.S. Pat. No. 2,313,598, issued to H. Stock on Mar. 9, 1943, and in U.S. Pat. No. 4,005,525, issued to D. Gringer on Feb. 1, 1987. In Stock, a locking member is pivotally mounted to a first one of the casing halves. The other half is provided with a transverse stud adapted to engage an opening defined in the first half of the casing for protruding therefrom in order to be engaged and locked in a recess defined in the locking member upon the pivot thereof. In Gringer, the two casing halves are resiliently secured together. A protrusion is included on one half to provide a finger pull to overcome the resiliency and to thus divergingly separate the two casing halves. From the above, there is a need for a safer and sturdier locking mechanism for the two halves of the casing. Furthermore, it is often difficult to initiate the pivot of one half with respect to the other especially if the two casing halves mate well together when they are in their aligned, functional and handle-like position.